1. Field of the Invention
The present invention concerns the dyeing and printing of synthetic fibers by means of disperse dyes, as well as the preparation of ready-to-use colorant compositions containing disperse dyes.
2. Description of the Prior Art
It is well known that during the process of dyeing, many disperse dyes undergo a chemical attack by the dyeing medium, this attack being generally considered as a hydrolysis, a reduction or an oxidation of certain less stable groups in the dye molecule. A detailed list of such dyes can be found, for example, in the "Color Index," Vol. 2, Third Edition, pages 2479-2791, and also in the paper of B. L. Neal, given on September 21, 1973 at the National Convention of the AATCC, entitled "Characteristics of Disperse Dyestuffs for Dyeing Texturized Polyester."
It is likewise known that the appearance of these secondary reactions, which are undesirable at the moment of dyeing, depends from a practical point of view on the nature of the auxiliaries currently employed in the dyeing industry, on the temperature, and particularly on the pH of the dyebath. Finally, certain fiber blends have been cited as being responsible for a marked degradation of the dyestuffs at the boil. There results from this a reduction in the tinctorial yield and/or a variation in shade of the dyed materials.
This sensitivity is thus a serious disadvantage which limits the utilization of certain disperse dyes, or which even prevents the utilization of new dyes which are too sensitive although in other respects entirely noteworthy.
Faced with this situation, the dyestuff producers more often than not have open to them only the course of recommending to users particular, and often draconian, conditions of application, principally as concerns the pH level in use, which has to be regulated in a precise manner. Many examples can be found of this in the commercial documentation of the different dyestuff manufacturers.
It has likewise been proposed in French Pat. No. 2,055,011 filed July 10, 1970 to use in the dyebaths certain water-soluble esters of carboxylic acids. However, these organic compounds are used in large amounts, such that this does not permit the preparation of ready-to-use colorant compositions, and this considerably increases the user's costs for the dyeing operation.